1. Technical Field
The present invention relates to check valves having a removable valve seat and, more particularly, to an improved method and apparatus for positionally securing and removing the valve seat and its associated clapper.
2. Discussion of the Prior Art
Check valves of the clapper type are often constructed in a manner requiring the valve housing to be disassembled in order to provide access to the valve interior for maintenance and repair. For example, in U.S. Pat. No. 3,955,592 (Guyton), the check valve embodiment illustrated in FIG. 1 therein has a two-part housing wherein the inlet port is provided in one housing part and the axially aligned outlet port is defined in the other housing part. Once the housing parts are disassembled, the clapper assembly can be lifted out of a specially designed hanger unit and, thereafter, the valve seat can be threadedly disengaged from the first body part. Another valve, illustrated in FIG. 6 of the Guyton patent, requires the same two body parts but, once those parts are disassembled, the clapper and hanger assembly can only be removed by removing threaded bolts, and the valve seat can be removed only by loosening a recessed set screw that radially bears against the seat periphery in an annual groove defined in the seat. The set screw and valve seat are inaccessible when the valve body parts are assembled. In many cases these valves are installed at sites where disassembly of the body parts is difficult at best and, in any event, requires the flow line to be shut down for long periods of time during maintenance and repair.
Certain prior art check valves are designed so that only a bonnet or cover need be removed to provide access to the housing interior, an example of such a valve being illustrated in FIG. 8 of the aforementioned Guyton patent. In that valve, once the bonnet is removed the clapper and hanger assembly can be removed by unscrewing a pair of threaded bolts that secure the hanger to the valve body. The valve seat is held in place by a recessed set screw bearing radially against the base of an annular groove defined in the valve periphery. Although this valve embodiment provides access to the valve interior without requiring the valve body to be disassembled, the removal of the valve seat is quite time consuming since the clapper and its hanger must first be threadedly disengaged. Then, the set screw that retains the seat must be withdrawn from the annular groove in the seat periphery. This procedure, although more efficient than disassembling the overall valve body, is nevertheless time consuming. Moreover, the set screw contacts the valve seat at a single location permitting pitch and yaw rotation of the seat relative to the flow path axis. Further, the annular groove defined in the valve seat: is wider than the set screw thereby permitting axial displacement of the seat relative to the set screw, a disadvantage that is aggravated by gradual loosening of the set screw due to vibration over a period of time. Any movement of the valve seat changes the mutual orientations of the clapper and seat, thereby jeopardizing the fluid seal between these elements.
It is known that valve seats for expanding gate valves can be removably mounted in the valve body with the aid of a pair of elongated retainer pins tangentially engaging the seat at diametrically opposed locations in an annular groove of the seat. For example, see U.S. Pat. No. 4,246,928 (Burns et al). The retainer pins are received in respective passages formed in the valve body, and threaded counterbores engage the threaded proximal ends of the pins. Each retainer pin has a flattened cut away portion where it engages the seat groove. This arrangement is designed to permit the seats to move axially to accommodate the varying positions of the gate members. In addition, even though the retainer pins can be loosened without removing the valve bonnet, removal of the valve seat requires the bonnet and its attached valve actuator assembly to be removed before the gate members can be likewise removed to provide access to the valve seats. Further, the requirement for separate passages for the retainer pins necessitates additional sealing gaskets and increases the possibility of leakage.